It has long been the practice in the construction of refractory kilns or furnaces and particularly high temperature units employed for metallurgical purposes, to fabricate the enclosure with heat resistant brick bodies partially or totally encased in a sheet metal envelope of sleeve. These brick bodies may be of various shapes with rectangular bricks, for example, being used in structures such as open hearth furnaces while tapered bricks are generally employed in refractory designs for electric furnaces.
U.S. Pat. No. 3,287,872 shows and describes one type of metal encased refractory brick wherein the encasing metal is mechanically attached to the brick body in surrounding relationship thereto. In the structure of this patent, segments of the casing extend inwardly from the metal jacket to provide for expansion and oxidation of the steel, but the assembly is expensive to manufacture, and has limited, if any, ability to prevent heat induced expansion spalling of the brick bodies since the latter are totally encased within sidewalls which engage all surfaces of the brick. As a consequence, when the encased bricks are laid in side-by-side relationship, there is still some tendency for the units to be subjected to undue compression load during heat induced expansion.
The same is true of the refractory brick shown and described in U.S. Pat. No. 3,566,571 wherein a brick body is enclosed within a metal casing having a series of dimples or spacing portions which engage respective brick walls either within complementary depressions therefor, or a planar sidewall of the brick. Here again, even though parts of the side sections of the metal casing are spaced from the adjacent wall surface of the refractory brick body, the dimples or spacing portions which are in engagement with the brick can exert compression forces thereon which are capable of inducing spalling during high temperature operations of the refractory constructed from such brick. Furthermore, manufacture of a brick as depicted and described in the U.S. Pat. No. 3,556,571 is relatively expensive and limits the market for such assemblies.
In U.S. Pat. No. 1,883,983, an attempt is made to thwart expansion spalling of brick by providing an asbestos filler material between adjacent brick bodies. Although this method may be effective in certain applications, the cost factor has militated against significant use thereof, particularly when the cost of installation of the brick is taken into account.